A condensate pump collects condensate water from the evaporator of the HVAC system and pumps the condensate water to a remote location for disposal. Particularly, a conventional condensate pump comprises a reservoir for collecting condensate water from the evaporator of the HVAC system, an impeller pump for pumping the water out of the reservoir to the remote location, and an electric motor to drive the impeller pump. A float in the reservoir detects the level of condensate water in the reservoir and activates control circuitry to control the operation of the electric motor.
In some smaller HVAC systems, the condensate pump may employ a solenoid pump, instead of an impeller pump, and a condensate water collection reservoir. In some instances, the solenoid pump and the reservoir may be separate. A conventional solenoid pump is designed to operate at a fixed AC input voltage and frequency, for example, standard household current of 120 volts at 60 Hz. Such a conventional solenoid pump 2 is shown in FIG. 1. The conventional solenoid pump 2 comprises a pump cylinder 4 with an inlet 6 and an outlet 8. A hollow cylindrical plunger 10 is slidably mounted within a pressure chamber 14 of the pump cylinder 4. The plunger 10 is driven toward the inlet 6 by means of an electromagnetic solenoid coil 22. The plunger 10 is driven toward the outlet 8 by means of a plunger spring 20. The plunger 10 has an internal plunger channel 12 which forms a communication channel between the inlet 6 and the pressure chamber 14 of the pump cylinder 4. A first check valve 16 engages the plunger channel 12 within the pressure chamber 14. A second check valve 18 seals the pressure chamber 14 adjacent outlet 8.
In operation, the electromagnetic solenoid coil 22 is connected through a diode to a source of AC current with a frequency of 50/60 Hz. The voltage from the source of AC current is shown as a full waveform 24 in FIG. 2. The voltage applied to the electromagnetic solenoid coil 22, as a result of the operation of the diode, is shown as a half wave rectified waveform 26 in FIG. 2. The half wave rectified waveform 26 has intake portions 28 and discharge portions 30. During intake portions 28 of the rectified waveform 26, the electromagnetic solenoid coil 22 is energized, and the plunger 10 is driven by the electromagnetic solenoid coil 22 toward the inlet 6. As the plunger 10 is driven toward the inlet 6 by the electromagnetic solenoid coil 22 (intake portion 28), the first check valve 16 allows entry of condensate water into the pressure chamber 14 of the pump cylinder 4, while the second check valve 18 precludes condensate water from flowing back into the pressure chamber 14 from the outlet 8. During discharge portions 30 of the rectified waveform 26, the electromagnetic solenoid coil 22 is de-energized, and the plunger 10 is driven by the plunger spring 20 toward the outlet 8. As the plunger 10 is driven toward the outlet 8 by the plunger spring 20 (discharge portion 30), the first check valve 16 seals the plunger channel 12 so that the condensate water in the pressure chamber 14 is forced through the second check valve 18 and out of the outlet 8.
Due to the electromagnetic effects of the electromagnetic solenoid coil 22, the mechanical harmonics with the plunger spring 20, and the dynamics of varying suction and discharge pressures, it is impossible for the prior art solenoid pump 2 connected to an AC current source through a single diode to operate efficiently under all conditions. Particularly, during the time in which the AC current in the electromagnetic solenoid coil 22 is driving the plunger 10 toward the inlet 6 (intake portion 28), current continues to flow into the electromagnetic solenoid coil 22 even after the plunger 10 has reached the end of its travel. The continuing application of current to the electromagnetic solenoid coil 22 after the plunger 10 has reached the end of its travel causes an unnecessary buildup of heat in the electromagnetic solenoid coil 22. Such a buildup of heat limits the range of voltages and frequencies over which the solenoid pump 2 will operate. In addition, using the half wave rectified waveform 26 causes the plunger 10 to slam into the end of the pump cylinder 4 at the end of the plunger's travel as the plunger 10 compresses the plunger spring 20. Consequently, the conventional solenoid pump 2 connected to a source of AC current through a single diode is noisy.